It is the time of year where most plants would have shut down in the Holiday Season. It is typical to have any time-consuming work accomplished during this period such as scheduled overhauls of any major equipment. Years ago, petfood processors determined once the equipment became durable enough to last a year the obvious point to prepare for the next year was during this break.
Wear on some machines is such that they need attention more than others. Hammermill screens, for example, need to be replaced as needed and thus quick changing screen machine designs help minimise down time. Machine design is usually constructed to have access for timely repairs.
What would be the top or most frequently changed parts in a modern petfood extrusion production facility? Knife blades are normally number one as product appearance is critical and seen right off and thus corrections are made. Today product quality is number one and this is an important fact in selecting the parts that should be on hand in the plant for replacement purposes. Let’s make lists by area. To start, the supplier of the gear should be the best source on the lifetime of their equipment and their parts: Raw material area, bearings, seals, lubricants, gears, motors, electrical components, and sensing gear. Yes, you can have too much but the idea is to develop a list that works for you based on down time related to when parts can be delivered. Standardisation in some cases can reduce spare parts held due to multiple use areas.
The processing area, mainly the extrusion equipment is where to place the most attention. Big heavy parts need planning to replace and availability. If there is one, the gear box on your extruder should have a lifetime rating, extruded screws and sleeves have expected wear lives. Dies do wear and the associated electrical, plumbing and control systems also have lists of parts to have on hand.
In many cases all of the above should be predictable by the equipment supplier, including predicted spare parts that should be on the shelf. With computer control systems the sensors and controls should be well covered. The computer control packaged worked with over the years have all had the ability to run if a sensor is out in most cases or a clued in sparky can temporarily jumper a bypass until the part is available.
The extruder barrel parts can be considered the hardest to get quickly due to many factors, such as availability, distance shipped, overseas paperwork etc. The amount of wear in this area is directly related to the running conditions, formulation, and its preparation. Everything seems to go hand in hand with production balanced for product quality, wear, operational costs etc. Then all becomes more predictable.
Studies years ago showed that feed performance, wear, utility, use as well as capacity and product quality were at its highest with lowest cost when running at about 22 to 30 percent moisture in the extruder. Lower moisture increased friction and increased vitamin losses, higher moisture reduced cook due to slippage in the barrel and thus both lowered feed performance. Typically, single screw extruders wear and when the initial gap between the screws and sleeves is 2 to 2.5 times the original then some of the screws need replaced. More on this next month.
